Micromechanical devices having a deflectable element such as a cantilever or membrane are used in a multitude of technical fields, such as in spatial light modulators or in projectors for beam deflection, just to mention a few examples.
Primarily, electrostatic attraction used in micro and nano actuators as the principle for deflection. Mostly, different electrostatic potentials are applied to a deflectable element and a static electrode so that by aid of an electrostatic attraction developing therebetween, a deflection is caused. The force is indirectionally proportional to the square of the distance between the deflectable element which serves as a first electrode and the second, static electrode. Owing to this relation, a pull-in effect manifests itself in case of exceeding a predetermined potential difference, wherein the deflectable element is accelerated towards the static electrode with contacting the latter. Due to this, using an electrostatic actuator involves the provision of sufficient distance between the static electrode and the deflectable element. This in turn increases the voltages to be applied in order to achieve a certain amount of deflection as the electrostatic force is lower for increased distances. Voltages up to 100 V or even more are not unusual. This causes even further problems.
Besides, there are also bimorph deflectable structures. Thermomechanic bimorph structures use, for instance, the different dilatation of materials by using heating structures, thereby exploiting the bimorph principle. Disadvantageously, however, the response is slow and high temperature differences may be used in order to achieve high deflections. Beyond this, the set of suitable materials is restricted. Another bimorph principle uses piezoelectric or electrorestrictive elements so as to deflect the deflectable element according to the bimorph principle. Here, dealing with the useful materials causes a problem since these materials hinder the usage of usual semiconductor fabrication processes. All in all, the production of such actuating structures is expensive. A solution to overcome the above identified problems is described in WO 2012 095185 A1. Here, electrostatic attraction between two electrodes forming a plate capacitor is used so as to deflect the deflectable element. The plate capacitor is arranged offset to the neutral of the deflectable element. The proximate electrode, i.e., the one arranged nearer to the neutral axis, and the distant electrode, i.e., the one arranged farther away from the neutral axis, are affixed to each other at segment boundaries so that applying a voltage between the electrodes results in the deflectable element deflecting owing to compressive and expanding lateral stresses manifesting themselves in the electrodes.
Unfortunately, even the manufacturing of micromechanical devices using the just outlined electrostatic bimorph actuator is demanding. Accordingly, it would be favorable to have concepts at hand which result in a more effective way of actively deflecting micromechanical devices.